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Thread: Basic Check Valve Question

  1. #1
    DIY Junior Member turkeyvulture's Avatar
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    Default Basic Check Valve Question

    I think this is an easy one. Does the typical residential submersible pump have a check valve built into it? I have heard that this is so, but then I always see another one just before the pressure tank, so why is that one necessary if there's one in the pump?

    Thanks for the Wells 101 advice!

  2. #2
    DIY Senior Member craigpump's Avatar
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    They are either part of the discharge or screwed into the discharge. Around here everyone puts a check on the tank as well, someplaces check valves on the tank are against code.

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    Jack of all trades DonL's Avatar
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    Sometimes a Check Valve on the top side is used when the Check Valve in the well won't hold pressure.

    That is a half-fast fix that is cheaper and easier than pulling the pump out of the well.
    Theory only works perfect in a vacuum.

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    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by DonL View Post
    Sometimes a Check Valve on the top side is used when the Check Valve in the well won't hold pressure.

    That is a half-fast fix that is cheaper and easier than pulling the pump out of the well.
    If the checkvalve in the pump doesn't hold, the line is no longer under pressure and could be under vacuum. If a leak develops, the vacuum can suck in surface water and contaminate your well, creating a health hazard.

    Sometimes a topside checkvalve is used with a snifter and a bleeder as an air maker for a hydro-pneumatic tank. Sometimes it is setup as a drainback for frost protection.

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by LLigetfa View Post
    If the checkvalve in the pump doesn't hold, the line is no longer under pressure and could be under vacuum. If a leak develops, the vacuum can suck in surface water and contaminate your well, creating a health hazard.

    Sometimes a topside checkvalve is used with a snifter and a bleeder as an air maker for a hydro-pneumatic tank. Sometimes it is setup as a drainback for frost protection.

    I can see it under Vacuum, but how would it suck in surface water if it is on the output of the pump.


    What am I missing ? And where would the leak have to be for it to suck in surface water ?
    Theory only works perfect in a vacuum.

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    DIYer, not in the trades LLigetfa's Avatar
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    Seriously, how would a vacuum suck? Is that a trick question? I don't know how to answer that in a way you'd understand. I don't know what you're missing.

    When you drink through a straw, that is a partial vacuum sucking.

    The leak would have to be underground where surface water is present.

  7. #7
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by LLigetfa View Post
    Seriously, how would a vacuum suck? Is that a trick question? I don't know how to answer that in a way you'd understand. I don't know what you're missing.

    When you drink through a straw, that is a partial vacuum sucking.

    The leak would have to be underground where surface water is present.

    It is not a trick question. lol

    If the leak is underground then the water would be contaminated even if the check valve was working.

    The Venturi affect would suck in the contaminated water when the pump was running.

    What does the check valve have to do with it ? That is what I must have missed.
    Theory only works perfect in a vacuum.

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  8. #8
    DIYer, not in the trades LLigetfa's Avatar
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    If there is no topside checkvalve, the water stays under pressure all the time, so well water would exit the leak continually. There is no "venturi effect" in normal piping to suck in ground water. You need to take a look at how a micronizer is made to understand the forces it takes to create a vacuum through a venturi.

    It is possible for a fitting to leak under vacuum but not leak under pressure.

  9. #9
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by LLigetfa View Post
    If there is no topside checkvalve, the water stays under pressure all the time, so well water would exit the leak continually. There is no "venturi effect" in normal piping to suck in ground water. You need to take a look at how a micronizer is made to understand the forces it takes to create a vacuum through a venturi.

    It is possible for a fitting to leak under vacuum but not leak under pressure.

    I understated what you are saying.

    But I would not call a leak in a pipe "normal piping". If the pipe was leaking there could be no vacuum.


    Thanks for the clarification.
    Theory only works perfect in a vacuum.

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  10. #10
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by DonL View Post
    If the pipe was leaking there could be no vacuum.
    I don't know if you are arguing semantics or just being belligerent. True, there cannot be a perfect vacuum since the water would turn to vapor and occupy some of the space.
    In the presence of a topside checkvalve, there most certainly can be a partial vacuum. The weight of the water falling back to the well would create it. It works on the same principle as a mercury barometer.

    Fill a garden hose with water. Leave one end open and put your thumb over the other end and climb a ladder or stairs, dragging that end of the hose with you so that the other end remains lower. When you release your thumb at the top of the stairs, you will experience the suction. This same suction can suck in contaminated ground water.

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